The present invention relates to a resinous composition comprising a combination of organic and inorganic colorants which composition has good color and low heat accumulating properties, and a method to make such a composition.
Dark colors are associated with hot temperatures. In dark colored plastic articles high temperature often leads to surface deformation, cracking, and expansion under solar radiation. Use of inorganic infrared reflecting (IRR) pigments has been described for example in R. F. Brady and L. V. Wake, “Principles and Formulation for Organic Coatings with Tailored Infrared Properties” in Progress in Organic Coatings, 20, 1992. While infrared (IR) reflective pigments provide benefits against thermal distortion and expansion problems, the achievable color space is limited to medium dark colors. For example a jet black color is not achievable in plastic articles with IR reflective pigments. In particular deep dark color (dark brown, dark green, dark blue, dark red and black) with L* value below 40 is not achievable in plastic articles by use of just IRR pigments. To obtain desired jetness (dark colors with L value below 30), a organic colorants have also been included in the compositions as described in U.S. Pat. No. 6,822,041. The disadvantage is that the organic colorants are known to have poor resistance to solar radiation and consequently have poor weathering properties.
In U.S. Pat. No. 6,366,397 a dark color is achieved in a plastic article using a multilayer system. A coating arrangement is described therein which has a higher reflection of sunlight in the IR range. A disadvantage here is that the arrangement must consist of two layers to function effectively. A white layer having high solar reflectance is required as the first or base layer. A darker colored layer is then applied onto this base layer. The disadvantage here is not only that two layers must be applied to achieve a dark surface having low solar absorption, but also that if damage occurs to the dark outer layer, a white layer then appears which will disturb the dark appearance. EP 1541636 describes the use of a combination of two inorganic pigments to obtain a low thermal storage thermoplastic resin with weather resistance and shock resistance properties.
It remains of interest, therefore, to develop compositions for plastic articles which have low L* value and also good resistance to solar radiation.